I have been scouring the internet and this forum and I feel like there is limited information on using LED lights in a planted tank. There are also few choices when it comes to LED light options (althought I just saw that current USA came out with and LED line that looks promising). LED technology seems promising due to the high lumens per watt, long bulb life and the energy saving.
I have a medium light 55Gal planted tank (120W Current USA SunPaq CF) that I have had mixed results with plants. I have always struggled with growing dwarf hairgrass for some reason. So I am starting an experiment of which I will post the results. I have ordered 5 patches of dwarf hairgrass and an additional LED light fixture.
I ordered a Aquaray grobeam500 (http://americanaquariumproducts.com/LEDLights.html) which is a 12 watt LED fixture with 5 emitters. I will be using this in addition to my 120watt fixture and since this fixture is much smaller I will be mounting directly over the planted area for the grass. I will let you all know how things progress.

I agree dale, after doing a lot of research most available LED lights appear to be virtually useless for a planted tank. Many give a lot of light and even a lot of lumens at a great dept but often not the right kind of light. Many do not have the proper PAR requirements for a planted tank. These seems to have the most promise. These have what is called a CREE emmitter which is supposed to be ideal for plant growth.
According to the site I posted earlier, Studies/Test in plant growth has shown a 12 Watt 6500K Full spectrum/daylight LED Surpassing a similar 175 Watt 6500K Full spectrum Metal Halide!!
Obviously the proof will be in the pudding. Also I will be running this in addition to my CF setup. I just planted the hairgrass a few hours ago and I will most likely recieve my lights on monday or tuesday. I took some pics and will compare weekly growth updates to see if the LED makes an improvement. As I mentioned before I have tried 2 times and failed with hairgrass and I know it is because my lighting was insufficient especially in the front of the tank. We will see.

Another persistant problem is the lack of truly well-designed, long-life LED rigs. Fluval produces an LED light rig billed for growing plants that certainly puts out quite a bit more light than even their T5HO systems, at a comparable pricepoint, and across the spectrums needed for plant growth.

In my experience, however, this causes more harm than good. The LEDs have short lifespans, either being cheaply assembled themselves or cheaply installed into the system, and whole bars are prone to failure. Worse, once failed, the LEDs cannot be replaced.

These LED light systems also don't achieve anywhere near the few years one would expect a diode to operate - my guess is this is because the LEDs are pushed quite a bit harder than maybe they should be, to achieve the necessary light levels._________________http://auditorandagentleman.blogspot.com - now with 100% more fish.
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